Electronic devices with frequency scan acceleration

Abstract

An electronic device having a radio is provided. When the radio boots up, the radio may search for downlink signals transmitted by a wireless base station. The device may generate a narrow set of candidate frequencies over which to search for the downlink signals by leveraging a cyclic prefix autocorrelation property of the downlink signals. Each candidate frequency may have a corresponding center frequency offset (CFO) and symbol boundary timing correction that is used when searching over the narrow set of candidate frequencies. To generate the narrow set of candidate frequencies, control circuitry may generate autocorrelated signals from baseband-shifted input signals over a set of different center frequencies and bandwidths. Searching over the narrow set of candidate frequencies may be significantly faster than performing a full raster scan over all frequencies supported by the radio.

What is claimed is: 
     
         1 . Wireless circuitry comprising:
 a radio configured to receive radio-frequency signals via one or more antennas and configured to downconvert the radio-frequency signals to generate baseband signals; and   one or more processors configured to
 apply a bandwidth filter to the baseband signals to generate filtered baseband signals, 
 switch the bandwidth filter between bandwidth configurations over time, 
 generate respective autocorrelation metrics based on the filtered baseband signals under each of the bandwidth configurations of the bandwidth filter, and 
 perform a search for a wireless base station based on the autocorrelation metrics, wherein the radio is configured to establish a link with the wireless base station in response to the search detecting a signal transmitted by the wireless base station. 
   
     
     
         2 . The wireless circuitry of  claim 1 , the one or more processors being further configured to:
 generate respective coherent sums based on each of the autocorrelation metrics, and   perform the search for the wireless base station based on the coherent sums.   
     
     
         3 . The wireless circuitry of  claim 2 , the one or more processors being further configured to:
 identify a respective peak in each of the coherent sums and a respective sample number associated with each of the peaks, and   perform the search for the wireless base station based on the sample numbers.   
     
     
         4 . The wireless circuitry of  claim 3 , the one or more processors being further configured to:
 correct a symbol boundary timing of the radio-frequency signals based on the sample number identified for a highest of the peaks.   
     
     
         5 . The wireless circuitry of  claim 3 , the one or more processors being further configured to:
 identify a phase of a highest of the peaks, and   apply a center frequency offset to the radio-frequency signals based on the phase of the highest of the peaks.   
     
     
         6 . The wireless circuitry of  claim 1 , the one or more processors being further configured to:
 generate a set of cyclic prefix hypotheses and a set of coherent sums for the set of cyclic prefix hypotheses, and   perform the search for the wireless base station based on the set of coherent sums.   
     
     
         7 . The wireless circuitry of  claim 6 , the one or more processors being further configured to perform the search for the wireless base station based on a cyclic prefix hypothesis from the set of cyclic prefix hypotheses that corresponds to a maximum coherent sum in the set of coherent sums. 
     
     
         8 . The wireless circuitry of  claim 1 , the one or more processors being further configured to generate the autocorrelation metrics by autocorrelating samples from the filtered baseband signals in a time domain. 
     
     
         9 . The wireless circuitry of  claim 8 , the one or more processors being further configured to:
 perform the search for the wireless base station based on a set of cyclic prefix hypotheses that is based on a highest of the autocorrelation metrics.   
     
     
         10 . The wireless circuitry of  claim 9 , the one or more processors being further configured to:
 perform the search for the wireless base station based on a set of coherent sums that is based on the set of cyclic prefix hypotheses.   
     
     
         11 . The wireless circuitry of  claim 10 , the one or more processors being further configured to:
 perform the search for the wireless base station based on a set of frequency candidates that is based on the set of coherent sums.   
     
     
         12 . The wireless circuitry of  claim 11 , wherein the radio is configured to receive the radio-frequency signals over the set of frequency candidates, the one or more processors being further configured to perform the search for the wireless base station based on the radio-frequency signals received over the set of frequency candidates. 
     
     
         13 . The wireless circuitry of  claim 12 , wherein the radio is further configured to modify at least some of the radio-frequency signals received over the set of frequency candidates using a symbol boundary timing correction, the symbol boundary timing correction being based on the set of coherent sums. 
     
     
         14 . The wireless circuitry of  claim 12 , wherein the radio is further configured to modify at least some of the radio-frequency signals received over the set of frequency candidates using a center frequency offset, the center frequency offset being based on the set of coherent sums. 
     
     
         15 . The wireless circuitry of  claim 8 , wherein the one or more processors are further configured to:
 generate a first of the autocorrelation metrics by autocorrelating the filtered baseband signals as output by the bandwidth filter while the bandwidth filter exhibits a first bandwidth configuration,   generate a second of the autocorrelation metrics by autocorrelating the filtered baseband signals as output by the bandwidth filter while the bandwidth filter exhibits a second bandwidth configuration that is different from the first bandwidth configuration, and   perform the search over a set of frequency candidates that is selected based on a higher of the first of the autocorrelation metrics and the second of the autocorrelation metrics.   
     
     
         16 . The wireless circuitry of  claim 15 , wherein the one or more processors are further configured to generate select the set of frequency candidates based on:
 a statistical downlink signal model, and   a center frequency correction that is based on the statistical downlink signal model, wherein the radio is further configured to modify at least some of the radio-frequency signals received over the set of frequency candidates using the center frequency correction.   
     
     
         17 . The wireless circuitry of  claim 1 , wherein the radio is further configured to:
 modify at least some of the radio-frequency signals using a symbol boundary timing correction, the symbol boundary timing correction being based on the autocorrelation metrics, and the one or more processors being further configured to perform the search for the wireless base station by searching for the signal in the radio-frequency signals modified using the symbol boundary timing correction.   
     
     
         18 . The method of  claim 1 , the one or more processors being further configured to generate one of the autocorrelation metrics by multiplying each sample in a series of samples in the filtered baseband signals by a respective additional sample located at a fixed sample number from that sample in the series of samples. 
     
     
         19 . A method of operating wireless circuitry, the method comprising:
 receiving, using a radio, radio-frequency signals;   converting, using the radio, the radio-frequency signals into baseband signals;   generating filtered baseband signals by applying a bandwidth filter to the baseband signals;   switching the bandwidth filter between different bandwidth configurations over time;   outputting, using one or more processors, a different respective autocorrelation metric based on the filtered baseband signals that are generated while the bandwidth filter exhibits each of the different bandwidth configurations;   performing, using the radio, a search for a wireless base station based on the different respective autocorrelation metrics; and   establishing, using the radio, a link with the wireless base station in response to the search detecting a signal transmitted by the wireless base station.   
     
     
         20 . A method of operating wireless circuitry, the method comprising:
 receiving, using a radio, radio-frequency signals;   converting, using the radio, the radio-frequency signals into baseband signals;   generating first filtered baseband signals by applying a bandwidth filter to the baseband signals while the baseband filter has a first bandwidth configuration;   generating second filtered baseband signals by applying the bandwidth filter to the baseband signals while the baseband filter has a second bandwidth configuration that is different than the first bandwidth configuration;   outputting, using one or more processors, a first autocorrelation metric based on the first filtered baseband signals;   outputting, using the one or more processors, a second autocorrelation metric based on the second filtered baseband signals;   performing, using the radio, a search for a wireless base station over a set of candidate frequencies that is selected based on a higher of the first autocorrelation metric and the second autocorrelation metric; and   establishing, using the radio, a link with the wireless base station in response to the search detecting a signal transmitted by the wireless base station.